In the third year work will be directed to 3 areas. Firstly, we will continue the analysis of ion saturation effects in the voltage clamped frog endplate, using lithium, ammonium and calcium. Also, QX-222 kinetics in these solutions will be measured. Secondly, rapid flow desensitization measurements at a variety of agonist concentrations will be made. The influence of internal calcium on these properties will be determined using iontophoretic injection and arsenazo measurement. Thirdly, we will determine the agonist concentration dependence of spontaneous noise spectral parameters, to elucidate the kinetics of channel opening.